1. Field of the Invention
This invention relates to a wide angle optical system and an image pickup apparatus using the same. Especially, this invention relates to a small wide angle optical system which is favorable for photographing an object which is located at a relatively close position and relates to an image pickup apparatus using the same.
2. Description of the Related Art
As cellular phones, mobile terminals, and notebook computers have become thinner recently, the thin apparatuses require a camera module which is thinned in the direction of the length along the optical axis of the optical system to the utmost limit.
In order to meet the requirement, a large number of single-focus optical systems which are composed of about two or three aspherical lenses have been proposed for the purpose of using the single-focus optical systems for a camera module.
There is also a proposal to use for a camera module an image pickup element which has been developed in recent years and the sensitivity of which is not deteriorated by light which is slantingly incident on the periphery of the image pickup element. The use of such image pickup element for a camera module makes it possible to bring an exit pupil position of an optical system near to the image pickup element, so that it is possible to shorten the total length of the optical system by the use of the image pickup element. As a result, it is possible to thin the camera module. This is the reason why the use of such image pickup element for a camera module has been proposed.
Japanese Patent Kokai No. 2007-3768, Japanese Patent Kokai No. 2007-47513, and Japanese Patent Kokai No. 2007-58153 disclose an optical system which is composed of three lenses and in which an exit pupil position is nearer to an image pickup element, as one example of such optical systems. The optical system which is disclosed in the patent literatures is made as a telephoto type optical system in which a positive lens, a negative lens, and a negative lens are arranged in order from the object side of the optical system, with the aim of shortening the total length of the optical system more.